Astrobiology's most intensive effort at the moment is focused on Mars, where NASA's robotic lander Phoenix is digging up soil and ice in a search for organic material.
(Bill Ingalls - Associated Press)

When Paul Butler began hunting for planets beyond our solar system, few people took him seriously, and some, he says, questioned his credentials as a scientist.

That was a decade ago, before Butler helped find some of the first extra-solar planets, and before he and his team identified about half of the 300 discovered since.

Biogeologist Lisa M. Pratt of Indiana University had a similar experience with her early research on "extremophiles," bizarre microbes found in very harsh Earth environments. She and colleagues explored the depths of South African gold mines and, to their great surprise, found bacteria sustained only by the radioactive decay of nearby rocks.

"Until several years ago, absolutely nobody thought this kind of life was possible -- it hadn't even made it into science fiction," she said. "Now it's quite possible to imagine a microbe like that living deep beneath the surface of Mars."

The experiences of these two researchers reflect the scientific explosion taking place in astrobiology, the multi-disciplined search for extreme forms of life on Earth and for possibly similar, or more advanced, life elsewhere in the solar system and in distant galaxies.

The confidence that alien life will ultimately be found is strong enough to have kindled formal discussions among scientists, philosophers, theologians and others about the implications that such a find would have for humanity's view of itself, and how to prepare the public for the news, should it come.

"There's been a fundamental shift in the thinking of the scientific community on the question of life-forms beyond Earth," Pratt said.

Edward J. Weiler, one of the founders of NASA's astrobiology program and now chief of the agency's science division, goes even further.

"We now know the number of stars in the universe is something like 1 followed by 23 zeros," he said. "Given that number, how arrogant to think ours is the only sun with a planet that supports life, and that it's in the only solar system with intelligent life."

Although humans have speculated for centuries about the possibility of extraterrestrial life, astrobiology began as a formal NASA program only in the mid-1990s, created in the excitement that followed the discovery of a meteorite from Mars that was initially thought to contain fossils or other evidence of microscopic organisms (a conclusion now generally rejected). The field has nonetheless grown quickly. More than 700 scientists and graduate students -- including molecular biologists, chemists, planetary scientists and cosmologists -- showed up at a NASA-sponsored astrobiology conference in California this past spring.

Many schools have growing astrobiology programs, and planet-hunter Paul Butler often travels from his base at the Carnegie Institution in the District to Chile, Hawaii and Australia to work with other astronomers at big telescopes. He estimates that 1,000 to 2,000 scientists now work in the field.

Few believe that the discovery of extraterrestrial life is imminent. However, just as scientists long theorized that there were planets orbiting other stars -- but could not prove it until new technologies and insights broke the field wide open -- many astrobiologists now see their job as to develop new ways to search for the life they are sure is out there.